This invention relates to an aerodynamically controlled, universally mounted, telescoping refueling boom for transfering fuel in flight from a tanker airplane to a receiver airplane.
While the primary use of the present invention is in the field of inflight refueling of aircraft it would apply equally to any similarly deployed boom or strut for any other purpose. Currently, various systems are used for the inflight refueling receiver aircraft by another tanker aircraft. One system employs a drogue/probe device, where the receiver aircraft includes a probe which is literally flown into a drogue unit. The drogue is a funnel-shaped receptacle attached to a long hose suspended from the tanker aircraft. While the system has enjoyed some success, it requires the various receiving aircraft to be capable of rather precise control, and carry a fixed or telescoping boom to support the probe. Since the refueling hose must be extended and retracted from the tanker, as on a reel, the hose must be small in diameter, severely restricting the rate of refueling.
Another system currently in vogue comprises a boom which extends downwardly and rearwardly from the tanker aircraft. The receiver aircraft connects to a nozzle located at the end of the boom. This invention relates to this type system and is directed to improving the boom design, the boom attachment means to the tanker structure, and the means for aerodynamically controlling the boom.
There are four known U.S. patents which disclose aerodynamically controlled, universally mounted, telescoping refueling booms; U.S. Pat. Nos. 2,663,523 LEISY I; 2,670,913, CASTOR ET AL; 2,960,295, SCHULZE; and 2,859,002, LEISY II. All four references disclose a two-axis pivot means for attaching the boom to the tanker wherein lateral or sideward displacement of the boom occurs about a vertical axis. This motion provides a true yawing boom, with the long boom dimension exposed to the air stream, and the resulting large yawing moments which resist the rotation. The first three references disclose a universal type pivot mount generally as shown in FIG. 2. The fourth reference provides a gimbal-type pivot mount wherein the two mutually perpendicular axes of rotation lie in a single plane; however, lateral displacement of the boom still occurs about a vertical axis. The last reference, LEISY II, further teaches a third axis of control about the longitudinal center line of the boom. The roll axis, as taught in LEISY II, is not fixed in relationship to the fuselage centerline but rotates with motion about either of the other two axes of motion. The boom is allowed to swing both laterally and vertically without restraint. However, rotation of the boom about its longitudinal axis is, and must be, controlled. The control in the roll axis is essential because the boom is a well faired aerodynamic section, which is in effect a thick high aspect ratio wing which is twisted or rotated so as to develop sideward lift and thereby control lateral displacement of the boom. As taught, the vertical vane on the boom is removed and the sideward lift provided by the rotated boom is the sole force to control lateral displacement of the boom.
Prior art refueling booms have problems of maneuverability owing principally to the high cross-flow drag of the thick boom sections, particularly at large lateral or yaw deflections and high mach numbers. The prior art employs boom sections which are thick ellipses which provide some drag and air-loads reduction when the boom is rotated in the plane of symmetry of the tanker or the pitch plane of the boom. However, further streamlining of the boom section would increase the chord axis of the boom and since lateral or yaw displacement of the boom occurs about a vertical axis further increasing the chord would further increase already large yawing moments which resist the lateral displacement of the boom. Furthermore, increasing the chord would increase an already thick wake downstream of the yawed section and would further limit the effectiveness of the control vanes.
Another source of deficiency in the prior art is the "vee" control vane configuration. This configuration suffers from high induced drag and low effectiveness when operating as a rudder with large differential deflections required to trim the large sideloads when the boom is yawed to its limits. The "vee" type vane configuration also requires a bulbous fairing around the wide bearing mounts required to support the cantilevered control surfaces and clearance cutouts which further disturb the airflow around the vanes.
The primary object of this invention is to reduce the boom aerodynamic cross-flow drag and to accomplish same without the addition of mechanisms, controls or heavy fairings. This objective is best accomplished by providing a boom motion which allows the use of a more ideally faired boom section which is maintained closely aligned with the air stream.
A further objective of the invention, and as a result of the reduction in air load and the constant alignment of the boom section with the air stream, is to provide smaller control vanes of a more practical and efficient configuration.